Thin film techniques are widely developed for miniaturization and performance enhancement of devices. Devices in the form of a thin film not only provides a direct advantage for users but also plays an important role from an environmental viewpoint, for example, in conserving the earth resources or reducing power consumption.
For such development in thin film techniques, it is indispensable to satisfy requirements in view of industrial availability such as efficiency enhancement, stabilization, productivity enhancement, and cost reduction in the thin film-manufacturing method, for the purpose of which efforts have been continuously made.
In order to enhance the productivity of thin films, film-forming techniques at high deposition rates are essential. In thin film-manufacturing methods such as vacuum evaporation, sputtering, ion plating, CVD (Chemical Vapor Deposition), the deposition rate is progressively enhanced. Further, a thin film-manufacturing method of the take-up type is used as a method for continuously forming thin films in large scale. The thin film-manufacturing method of the take-up type is a method in which an elongated substrate wound into a roll is unwound from an unwinding roller to form a thin film on the substrate during the conveyance along a conveyance system, and thereafter the substrate is wound by a winding roller. For example, thin films can be formed with good productivity by combining a film-forming source that allows high deposition rate such as vacuum evaporation using an electron beam with the thin film-manufacturing method of the take-up type.
There are problems of thermal load during film formation and cooling of the substrate as factors that determine the success or failure of the continuous thin film production of the take-up type. For example, in the case of vacuum evaporation, thermal radiation from an evaporation source and thermal energy of evaporated atoms are applied onto a substrate, thereby increasing the temperature of the substrate. Also in other film-forming methods, a thermal load is applied, though the heat source is different, onto a substrate during film formation. The substrate is cooled in order to prevent such thermal load from causing the deformation, melting down, etc., of the substrate. The cooling is not necessarily carried out during film formation, and may be carried out on a substrate-conveyance channel other than the film-forming region.
As a method for cooling a slurry, etc., in the ambient atmosphere using a roller, Patent Literature 1 discloses a cooling roller characterized by providing a number of slits or holes on the cylinder wall of a cylindrical body, providing a partition plate inside the cylindrical body so as to allow the cylindrical body to slidably rotate with respect to the partition plate, and providing a cooling gas injection tube in one chamber partitioned by the partition plate. According to this configuration, it is possible to cool the slurry by spraying a large amount of cooling gas onto the slurry so as to conduct heat away from the slurry directly.
However, in order to maintain vacuum atmosphere, the use of such a large amount of cooling gas that directly removes heat is not permitted. For example, as a cooling method of a substrate during film formation, film formation on a substrate extending along a cylindrical can disposed on a channel of a conveyance system is widely employed. According to this method, it is possible to release heat to the cooling can with a large heat capacity by ensuring a thermal contact between the substrate and the cylindrical can, thus preventing an increase in the temperature of the substrate. Further, it is possible to maintain the temperature of the substrate to a specific cooling temperature. The substrate can be effectively cooled by a cooling can also in a region other than the film-forming region on the substrate-conveyance channel.
As a method for ensuring the thermal contact between the substrate and the cylindrical can, gas cooling can be employed. Patent Literature 2 discloses that, in an apparatus for forming a thin film on a web as a substrate, a gas is introduced into a region between the web and a support means. According to this configuration, it is possible to ensure heat conduction between the web and the support means, thus suppressing an increase in the temperature of the web.
On the other hand, a cooling belt can also be used instead of the cylindrical can as a means for cooling the substrate. In the case of film formation using obliquely incident components, it is advantageous to perform film formation onto the substrate running linearly, in view of material use efficiency. In that case, a cooling belt can be used effectively as a substrate cooling means Patent Literature 3 discloses a method for cooling a belt when used for conveying and cooling a substrate material. According to the method disclosed in Patent Literature 3, when using a cooling belt for improving thin film-forming efficiency in a thin film-forming apparatus that generates a thermal load, a cooling mechanism using two or more cooling belts or a liquid medium is provided inside the cooling belt in order to cool it further. This can enhance the cooling efficiency, which thus makes it possible to improve the properties of a magnetic tape such as electromagnetic conversion characteristics, and to improve the productivity significantly at the same time.